More than 100 allegations of wrongdoing have been levelled against Police Scotland’s counter-corruption unit including claims officers attempted to pervert the course of justice, the force’s Chief Constable has admitted.

Phil Gormley said he has asked the Chief Constable of Durham Constabulary to review 25 complaints lodged against the unit between April 2009 and June this year involving 108 accusations for criminal and non-criminal behaviour.

Over that period there have been criminal allegations against officers relating to the data protection act and perverting the course of justice. Many of these relate to the "legacy" regional forces, prior to Police Scotland being set up.

In a letter to Holyrood’s justice committee, Mr Gormley disclosed that the files on many of the complaints have been closed but one case alleging corruption is live.

Derek Penman, HM Inspector of Constabulary in Scotland, criticised the unit as being “below standard” and made dozens of recommendations to bring it up to scratch and a judicial tribunal found it had acted “unlawfully”.

The data protection claims were reported to the Crown Office, but no proceedings were initiated by prosecutors. In his letter to the committee, Mr Gormley detailed the results of internal investigations into 17 complaints against the squad.

He said: “The Duties and Responsibilities allegations resulted in Management Action, the eight Neglect of Duty allegations resulted in corrective advice on six occasions and no action being taken in respect of the other two allegations.

“The six allegations of Wilful or Careless Falsehood resulted in corrective advice being provided on five occasions and no action being taken on the remaining allegation. One allegation related to Discreditable Conduct which resulted in no action.”

He said there was also a live investigation into one criminal allegation of attempt to pervert the course of justice and 11 non-criminal accusations.

The Interception of Communications Commissioner ruled in November 2015 that the unit’s actions actions while attempting to find the source of a newspaper story about the Emma Caldwell murder inquiry "could properly be seen as reckless".

An Investigatory Powers Tribunal later ruled that one former officer whose communications were intercepted as part of the probe should be paid £10,000 in compensation.

Neil Richardson, who was then a Deputy Chief Constable, told a Holyrood inquiry that the rules had been broken because of a “misjudgement” by an experienced officer.

MSPs were also informed that a disc containing CCTV evidence deemed important to the case was missing for some time, before it was eventually found in an officer's locker.